Process for electrodepositing manganese metal

ABSTRACT

The present invention relates to a process for producing electrolytic manganese metal. Broadly, the invention comprises adding trace amounts of selenium and zinc to the electrolyte of a manganese electrodeposition cell to increase the current efficiency of the cell. It has been discovered that a combination of zinc and selenium acts synergistically to increase the current efficiency of the cell.

[451 June 28, 1974 PROCESS FOR ELECTRODEPOSITING MANGANESE METAL [75]Inventor: San-Cheng Lai, Edmond, Okla.

[73] Assignee: Kerr-McGee Chemical Corp.,

Oklahoma City, Okla.

[22] Filed: Dec. 22, 1972 [2]] App]. No.: 317,526

[52] 11.8. CI 204/105 M [51] Int. Cl C22d l/24 [58] Field of Search 204/105 M [56] References Cited UNITED STATES PATENTS 3,455,799 7/1969Mantell et al. 204/105 M 3,696.01! lO/I972 Lai 204/105 M FOREIGN PATENTSOR APPLICATIONS 15,610 1/1970 Japan 204/105 M 19,282 9/I966 Japan204/l05 M Primary Examiner-John H. Mack Assistant Examiner-R. L. AndrewsAttorney, Agent, or Firm-William G. Addison 57 I ABSTRACT 7 Claims, N0Drawings PROCESS FoR ELECTRODEPOSITING MANGANESE METAL BACKGROUND OF THEINVENTION It is well known that in the electrodeposition of manganesemetal, that the addition of a small amount of sulfur dioxide to theelectrolyte helps to prevent oxidation of the manganous ion in thesolution and reduces the undesired formation of manganese dioxide on theanode. However, in commercial practice when sulfur dioxide is used as anadditive, it has been found that current efficiencies in the cell areonly about 60-65%.

In U.S. Pat. No. 3,455,799 it is suggested that the addition of a smallamount of zinc ions to a catholyte in a manganese electrodeposition cellwill reduce the current density necessary to produce manganese.Patentees further disclose that their invention enables inputrequirements of the cell to be reduced whereby operating efficiency isincreased. However, in tests using zinc as the additive, it has beenfound that the current efficiency is increased by only about I to 2percent.

In an article Effect of Selenious Acid on the Electrodeposition ofManganese, by A. J. Rao, Y.D.P. Rao, and R. Vedaraman, published in theNovember- December, 1966 (Volume 4) issue of the Journal ofElectrochemical Technology it was reported that when The presentinvention comprises an improved process for the electrodeposition ofmanganese. The improvement comprises adding to the electrolyte of amanganese electrodeposition cell a combination of zinc and selenium inan amount sufficient to provide from 1 to 8 ppm selenium and from about1 to 5 ppm zinc.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention providesan improved process for the production of electrolytic manganese. Theproduction of manganese by the electrolysis of an aqueous electrolytecontaining manganese ions is well known to those versed in the art. Thepresent invention contemplates those processes wherein the electrolyteis mainselenious acid was used as an additive in place of sulfur dioxidein the electrodeposition of manganese metal that current efficiencies inexcess of 90% could be obtained. Further, it has been reported thathigher current densities can be used when selenium is used as theadditive and that its use results in'lower cell voltages when comparedwith conventional sulfate bath electrolytes wherein sulfur dioxide isused as the addition agent.

In U.S. Pat. No. 3,696,01 1 it is reported that when a selenium compoundis used as the additive, a precipitate of amorphous selenium forms inthe electrolyte. This is disadvantageous, of course, because theselenium is thereby removed from the electrolyte solution and theadvantages of its presence are lost, thus necessitating a constantreplenishment of selenium to the electrolyte. Further, costs areincreased because of the necessity of having to replace the seleniumwhich is precipitated out of the solution. Patentees suggest theaddition of small amounts of S0 to the,electrolyte to maintain theselenium compound in solution. However, the use of substantialquantities of a selenium compound as an additive to a manganeseelectrodeposition cell results in selenium contamination of the productmanganese.

SUMMARY OF THE INVENTION The present invention provides a processwhereby it is possible to use selenium as an additive in theelectrodeposition of manganese with substantially no seleniumcontamination of the electrodeposited manganese. Broadly, the presentinvention is based upon the discovery that the addition of a combinationof zinc and selenium in only trace amounts provides a substantialincrease in the current efficiency of a manganese electrodepositioncell. Further, when zinc and selenium are used in the amounts set forthherein substantially no selenium contamination of the electrodepositedmanganese is observed.

tained at a pH of from about 7 to 8.5 and contains ammonium sulfate inan amount of from about to grams per liter and from about 11 to 45 gramsper liter of manganous ion. Generally, in such processes the manganeseis electrodeposited at a cathodic current density of from about 35 to 55amps per square foot.

In accordance with the present invention it has been discovered thatwhen two known additives, selenium and zinc are added to such anelectrolyte they act synergistically to increase the'current efficiency.Thus, it now is possible to obtain a substantial increase in currentefficiency while adding only trace amounts of additives to theelectrolyte.

The selenium compounds which are suitable for use in the presentinvention are selenious acid (H SeO or other selenium compounds such as,for example, 5e0 S603, Nagsfiog, (NH4)ZSCO3, Na ScO (NH4)2SeO and thelike. Other compounds contemplated herein include Selene-organics suchas, for example, selenourea, selenoguanidine, phenylselenourea,tributylselenophosphate and the like. Further, aromatic and quaternaryselenium compounds also may be used. These compounds may be added to theelectrolyte directly or fed in continuously as aqueous solutions. Theconcentration of selenium may be present in an amount of from about 1 to8 parts per million (ppm). However, it is preferred that theconcentration of selenium be from about 1 to 5 ppm.

' Zinc also is added to the electrolyte in an amount sufficient toprovide a concentration of zinc ion in an amount of from about 0.1 to 5ppm and preferably in an amount sufficient to provide a concentration offrom about 0.3 to 2 ppm. The zinc is added in any form of compound thatwill disassociate in the electrolyte to provide zinc ions in solution.Examples of such compounds include zinc sulfate, zinc chloride, zincsulfite and zinc ammonium chloride. The concentration of zinc ion shouldnot be allowed to exceed about 5 ppm, as it has been observed that ahigher concentration of zinc may result in a decrease in currentefficiency. Particularly, good results have been obtained when theconcentration of zinc ion is in the range of from 0.5 to 1 ppm and theweight ratio of zinc ion to selenium is about 1:3.

Advantageously, sulfur dioxide also is added to the electrolyte. It maybe supplied by bubbling liquified or gaseous S0 into the electrolyte orby adding to the electrolyte compounds such as H SO Na SO (NH SO and thelike which may be converted to S0 in the electrolyte. Generally, theconcentration of S0 is maintained within the range of from about 0.1 to1.0 gm/liter. However, the best results have thus far been obtained whenthe S is present in an amount of from about 0.1 to 0.5 gm/liter.

EXAMPLE To demonstrate the effectiveness of the present invention, aseries of electrodepositions of manganese metal are performed withvarious amounts of zinc and selenium as additives to an electrolyte. Theelectrolysis conditions are as follows:

Temp. 34 C.

Current density 45 asf.

The initial electrolyte consisted of:

Mn++ l4 gm/l Oz 4 140 gm/l S0 0.4 gm/] The results of the tests are asshown in the following table.

Selenium content not determined.

From these tests it is seen that the addition of trace amounts of acombination of zinc and selenium to the electrolyte provides an increasein current efficiency that is greater than the sum of the increases incurrent efficiency obtained when they are used individually. Further,when the concentration of selenium is maintained within the range offrom about 1 to 8 ppm substantially no selenium contamination of theelectrodeposited manganese is observed.

The composition of the electrolyte is not critical to the operability ofthe present method. However, it has been noted that the concentration ofmanganous ion in the electrolyte does have an effect on the amount ofsynergism observed using the additive combination of the presentinvention. More particularly, at a manganous ion concentration in excessof about 25 gm/l little synergism is observed. Therefore, to obtain fullbenefit of the present invention it is preferred to maintain themanganous ion concentration in the range of from about 14 to 25 gm/l.

The foregoing example and description are for the purpose ofillustration only and should not be considered as limiting the scope ofthe instant invention; reference being had to the appended claims forsuch latter purpose.

What is claimed is:

1. In a process for electrodepositing manganese metal from an ammoniumsulfate electrolyte containing manganese as manganous ion in an amountup to about 25 gm/l, the improvements which comprise introducing intosaid electrolyte a selenium compound in an amount sufficient to providefrom about 1 to 8 ppm of selenium and a zinc compound in an amountsufficient to provide from about 1 to 5 ppm of zinc ion based on thetotal volume of the electrolyte.

' 2. The process of claim 1 wherein the electrolyte contains sulfurdioxide in an amount of from about 0.1 to 1.0 gm per liter ofelectrolyte.

3. The process of claim 1 wherein the selenium compound is selected fromthe group consisting of H SeO S603, (NH )2SeO3, (NH4)2SeO3 and 8e02- 4.The process of claim 1 wherein said selenium is present in an amount ofabout 3 ppm of electrolyte and the zinc is present in an amount of about1 ppm of electrolyte.

5. The process of claim 1 wherein the electrolyte is maintained at a pHof from about 7.0 to 8.5 and contains ammonium sulfate in an amount offrom about 100 to 160 gm/l, sulfur dioxide in an amount of from about0.1 to 1.0 gm/l and manganous ion in an amount of from about 11 to 25gm/l, based on the total volume of electrolyte.

6. The process of claim 5 wherein the zinc and selenium are present inan amount within the range of from about 0.3 to 2 ppm and l to 5 ppmrespectively.

7. The process of claim 6 wherein the zinc and selenium are present inan amount sufficient to provide a weight ratio of zinc to selenium ofabout 1:3.

2. The process of claim 1 wherein the electrolyte contains sulfurdioxide in an amount of from about 0.1 to 1.0 gm per liter ofelectrolyte.
 3. The process of claim 1 wherein the selenium compound isselected from the group consisting of H2SeO3, SeO3, (NH4)2SeO3,(NH4)2SeO3 and SeO2.
 4. The process of claim 1 wherein said selenium ispresent in an amount of about 3 ppm of electrolyte and the zinc ispresent in an amount of about 1 ppm of electrolyte.
 5. The process ofclaim 1 wherein the electrolyte is maintained at a pH of from about 7.0to 8.5 and contains ammonium sulfate in an amount of from about 100 to160 gm/l, sulfur dioxide in an amount of from about 0.1 to 1.0 gm/l andmanganous ion in an amount of from about 11 to 25 gm/l, based on thetotal volume of electrolyte.
 6. The process of claim 5 wherein the zincand selenium are present in an amount within the range of from about 0.3to 2 ppm and 1 to 5 ppm respectively.
 7. The process of claim 6 whereinthe zinc and selenium are present in an amount sufficient to provide aweight ratio of zinc to selenium of about 1:3.